Assessing spinal deformity is of tremendous importance for a number of diseases affecting the human spine; one of them is scoliosis and its most common type, idiopathic scoliosis. Scoliosis is a disease that affects the human spine by introducing an abnormal lateral curvature, as observed in the frontal plane. The disease is typically detected during a standard physical examination. The routine procedure for assessing the severity of curvature is to use an anterior-posterior radiograph, where the Cobb angle is measured. See, R. Cobb, “Outline for study of scoliosis,” American Academy of Orthopedic Surgeons, Instructional Course Lectures, pp. 261-75, 1948. The Cobb angle is defined as the angle between the end vertebrae of the scoliotic curvature. There are other manual measurement methods for assessing frontal curvature and also sagittal curvature of the spine, but the Cobb angle is the most commonly used measure. The Cobb angle plays a significant role both when monitoring the disease and when selecting the appropriate treatment (bracing or surgery), even though it is well-established that the Cobb angle is insufficient both to describe and to properly quantify the deformity in scoliosis. This is due to the three dimensional (3D) nature of a scoliotic curvature, which may include a displacement, a rotation and/or a deformation of each vertebra. The Cobb angle particularly fails to measure the axial vertebral rotation, considered to be important for the assessment of spinal deformity in scoliosis.
Another limitation of the Cobb angle is its observer variability. Hence, other approaches for quantifying the degree of scoliosis are called for, including not only new quantitative measures but more importantly an analysis determining how different measures relate to each other and to the clinical outcome. See, Schwab et al., “Adult scoliosis: a quantitative radiographic and clinical analysis,” Spine, vol. 27, no. 4, pp. 387-392, 2002; Hong et al., “Evaluation of the three-dimensional deformities in scoliosis surgery with computed tomography: Efficacy and relationship with clinical outcomes,” Spine, vol. 36, no. 19, pp. E1259-E1265, 2011; and Easwar et al., “Does lateral vertebral translation correspond to Cobb angle and relate in the same way to axial vertebral rotation and rib hump index? A radiographic analysis on idiopathic scoliosis,” European Spine Journal, vol. 20, no. 7, pp. 1095-1105, 2011. This relationship of the different measures can be important in order to classify various sub-types of idiopathic scoliosis and to determine suitable treatments of the different sub-types.
There remains a need for automated methods which can reliably assess the 3D deformity of the spine in individual patients.